The present invention relates to a method and apparatus for sensing torque, and more particularly to a torque sensing apparatus and method for measuring torque in response to a saturation condition of a magnetic member.
Numerous torque sensing systems have magnetoelastic rings secured to a rotatable shaft. When torque is applied about a longitudinal axis of the shaft, the torsional stress of the shaft is transferred to the magnetoelastic ring. The torsional stress changes the magnetic permeability of the magnetoelastic ring, typically in an axial direction. The ring also provides a corresponding magnetic field. Many conventional torque sensing devices use sensor coils or integrated circuit sensors to detect the magnetic field or magnetic permeability of the ring. The sensors typically detect a change in impedance or a change in an induced voltage of sensor components according to the magnetic field provided by the ring. The amount of applied torque is determined in response to such changes detected by the sensor.
The present invention is directed to a torque sensing apparatus for sensing torque applied to an elongated shaft having a longitudinal axis. A magnetoelastic element is connected to a portion of the shaft. The magnetoelastic element provides a magnetic field in response to torque applied to the shaft. A magnetic member is positioned adjacent the magnetoelastic element. A source of alternating power repeatedly drives the magnetic member into magnetic saturation. The magnetic member has a saturation condition responsive to the magnetic field of the magnetoelastic element. A detector circuit detects the saturation condition of the magnetic member. The detector circuit provides a signal indicative of the applied torque in response to the saturation condition of the magnetic member.
Another aspect of the present invention is directed to a method for determining torque applied to an elongated shaft. The method includes the step of repeatedly driving a magnetic member into magnetic saturation. A magnetoelastic element is attached to the shaft. The method further includes providing a magnetic field in response to torque applied to the shaft. The magnetic member has a saturation condition responsive to the magnetic field. A signal indicative of the applied torque is provided in response to the saturation condition of the magnetic member.